Analogical electronic compasses have been known and have been commercially available for a long time. They comprise at least a saturable core sensor (flux-gate sensor) with a variable reluctance, whose output signals are correlated moment by moment to the angle comprised between the geographical North and the longitudinal axis of the vehicle (course angle); usually, the output signals of the sensor are respectively proportional to the sine and the cosine functions of the detected course angle. An electronic compass of this kind is disclosed in the European patent application EP-A-87890.
Said compasses usually make errors because of known or foreseeable reasons, such as, for instance, the magnetic deviation due to several elements. First of all, the earth's magnetic field is not homogeneous, but has a maximum intensity in the equatorial areas and a minimum intensity in the polar areas, showing also local distortions. Furthermore, the magnetic North does not coincide with the geographical North. Said errors can be avoided by suitably calibrating each compass. Especially during long trips, said lack of homogeneity in earth's magnetic field requires the frequent repetition of the calibrating process, which is usually long and expensive.
Another source of errors can be the supporting means connecting the compass to the boat, and keeping said compass, and in particular its sensor, in an horizontal position, or in any pre-arranged constant position, thus counterbalancing the heelings of the boat, or the sliding of the vehicle, due to the wave-motion and/or to the boat manoeuvres, for instance to a veer. If the heeling angle is larger than the maximum angle that may be counterbalanced by the supporting means, the compass, and in particular its sensor, follows the boat heeling, thus leaving the aforesaid pre-arranged position.
As a consequence, the intensity of the earth's magnetic field detected by the sensor is lower than, or different from the real one, and the compass “marks” a course angle which is different from the real one. This kind of error can be particularly relevant in the navigation on the high seas when the navigation is controlled by the automatic pilot, interlocked to the compass, which can consider the compass error as a course error, thus correcting it and leading the boat astray. In order to avoid this kind of errors, compasses usually hang from a support, such as a universal joint.
In order to allow the compass to work always with the same correctness, it must have a high angle sensitivity and good working dynamics, wherein angle sensitivity means the smallest angle the compass can detect, and working dynamics means the capability of maintaining the same sensitivity with varying conditions of the magnetic field.